A simple template engine in PHP

index.php

<?php
// 2015/07 :)
/**
 * The core class of Template Engine
 * Class templateEngine
 */
class templateEngine{
    /**
     * @type array
     */
    private $values = array();
    /**
     * Set template variable in server side
     * @param $property
     * @param $value
     */
    public function assign($property,$value){
        $this->values[$property] = $value;
    }
    public function display($file_name){
        $file       = file_get_contents($file_name);
        preg_match_all("/({(\s|\S)*?})/",$file,$commends);
        $var       = json_decode(json_encode($this->values));
        $var->_GET = $_GET;
        $file = str_replace("'","\\'",$file);
        foreach ($commends[0] as $commend) {
            $original   = $commend;
            $commend = ltrim(rtrim($commend,"}"),"{");
            $arg          = explode(" ",$commend);
            $function  = $arg[0];
            if($commend[0] === "$"){
                $args = $this->argCrater($commend);
                $commend = str_replace([",,",","],[".\" \".","."],$args);
                $file = str_replace($original,"'.".$commend.".'",$file);
            }
            if($function === "mod"){
                $commend = $arg[1]."%".$arg[2];
                $file = str_replace($original,"'.".$commend.".'",$file);
            }
            if($function === "set"){
                $n  = str_replace(".","->",$arg[1]);
                $var->$n = ltrim($commend,"set ".$arg[1]);
                $file = str_replace($original,null,$file);
            }
        }
        $file = "echo'".$file."';";
        eval($file);
    }
    private function argCrater($text){
        $args = explode(",",$text);
        $i = 0;
        foreach($args as $arg){
            if(@$arg[0] == "$"){
                $args[$i] =str_replace(
                    ["$","."],
                    ['$var->','->'],
                    $arg);
            }
            $i++;
        }
        $text = implode($args,',');
        return $text;
    }
}